CurvedAnimation class

CurvedAnimation is useful when you want to apply a non-linear Curve to
an animation object, especially if you want different curves when the
animation is going forward vs when it is going backward.

Depending on the given curve, the output of the CurvedAnimation could have
a wider range than its input. For example, elastic curves such as
Curves.elasticIn will significantly overshoot or undershoot the default
range of 0.0 to 1.0.

This second code snippet shows how to apply a different curve in the forward
direction than in the reverse direction. This can't be done using a
CurveTween (since Tweens are not aware of the animation direction when
they are applied).